The European Telecommunications Standard Institute—Digital Mobile Radio (ETSI-DMR) is a direct digital replacement for analog Private Mobile Radio (PMR). DMR is a scalable system that can be used in unlicensed mode (in a 446.1 to 446.2 MHz band), and in licensed mode, subject to national frequency planning. Any of the ETSI standards or specifications referred to herein may be obtained by contacting ETSI at ETSI Secretariat, 650, route des Lucioles, 06921 Sophia-Antipolis Cedex, FRANCE.
DMR promises improved range, higher data rates, more efficient use of spectrum, and improved battery. Features supported include fast call set-up, calls to groups and individuals, short data and packet data calls. Supported communications modes include individual calls, group calls, and broadcast calls provided via a direct communication mode among the radios operating within the network. Other important DMR functions such as emergency calls, priority calls, short data messages and Internet Protocol (IP)-packet data transmissions are also supported.
The ETSI-DMR standard provides for 6.25e (2:1 TDMA) operation in repeater mode. 6.25e operation refers to 6.25 Kilohertz (kHz) equivalent spectral efficiency and 2:1 refers to the slotting ratio supported on the TDMA air interface, in this case supporting two repeating (e.g., recurring) interleaved time slots. As there is no restriction on what happens in either time slot or any interrelation between them (other than the need to maintain time synchronicity), it is possible to have two entirely separate conversations at the same time from two different units. By this means it is possible that two simplex calls can be independently supported in a single 12.5 kHz channel.
FIG. 1 illustrates an example half duplex radio system 100. In a half duplex radio system, voice and/or data moves in only one direction at a time (source to target(s)), as compared to full duplex, in which voice and/or data can move in both directions (e.g., source to target(s) and target(s) to source).
The radio system 100 includes two radio sites 102, 104 coupled via a network 120. In site 1 102, a first repeater (repeater1) 110 and a second repeater (repeater2) 112 provide communications services to subscriber units (SUs) SU1 130, SU2 132, and SU3 154. In radio site 2 104, a third repeater (repeater3) 116 and fourth repeater (repeater4) 114 provide communications services to SUs SU4 140, SUS 142, and SU6 150. A controller 122 may control operations at sites 1 and 2 (102, 104), including the assignment of control and/or traffic channels at those radio sites.
Each of the repeaters 110, 112, 114, 116 may operate as a conventional repeater or a trunked repeater. In a conventional radio system, a plurality of SUs are formed into groups. Each group uses an associated channel (shared or separate) for communication. Thus, each group is associated with a corresponding channel, and each channel can only be used by one group at any particular moment in time. In some systems, multiple groups may operate on the same channel, and may use a unique group ID embedded in the group communications to differentiate them. In a trunked radio system, SUs use a pool of channels for virtually an unlimited number of groups. Thus, all groups are served by all channels. For example, in a trunking system, all SUs operating at a radio site idle on an initial designated control channel and when a new call is requested over the control or rest channel, is assigned a new traffic channel for the new group call while remaining SUs not participating in the new group call stay on the initial designated control channel. In other trunked configurations, the control channel is converted to a traffic channel for the new call, and the SUs not participating in the new group call move to a newly assigned control channel. In still other trunked configurations, the control channel is converted to a traffic channel for the new call, and the SUs not participating in the new call stay on the control channel but do not participate (transmit or receive/unmute) in the new call.
Other conventional and trunked configurations are possible as well.
In an example consistent with the ETSI-DMR 6.25e standard, the radio system 100 may be a trunked radio system, and controller 122 may have assigned SU1 130 to timeslot one (TS1) 134 of a 2:1 slot ratio TDMA first inbound frequency (frequency1) being served by repeater1 110 and may have assigned SU2 132 to timeslot two (TS2) 136 on the same frequency1. Further, controller 122 may have assigned SU3 154 to TS1 156 of a 2:1 slot ratio TDMA second outbound frequency (frequency2) being served by repeater2 112. The controller 122 may have also assigned SU4 140 and SUS 142, respectively, to TS1 144 and TS2 146 of a same 2:1 slot ratio TDMA third outbound frequency (frequency3) being served by repeater3 116. Finally, the controller 122 may have assigned SU6 150 to TS1 152 of a 2:1 slot ratio TDMA fourth inbound frequency (frequency4) being served by repeater4 114. In this example, SU1 130 may be transmitting voice data to SU4 via TS1 134 and TS1 144, SU2 132 may be transmitting voice data to SUS 142 via TS2 136 and TS2 146, and SU6 150 may be transmitting voice data to SU3 154 via TS1 152 and TS1 156. Voice and/or data received from SUs may be exchanged between repeaters 110-116 via interconnection network 120. The dispatch console 124 may operate as a client of the radio system 100, and provides a mechanism for a dispatcher to transmit or receive with one or more SUs at radio sites 1 and/or 2.
Although not illustrated in FIG. 1, additional control channel repeaters and respective control channels may be provided at each site 102, 104 as well. In other embodiments, one of the repeaters at each site (e.g., perhaps repeater1 110 and repeater3 116) may have acted as a control channel repeater prior to transitioning to a traffic channel repeater (trunked or single frequency repeater (SFR)) to handle a requested call.
In any event, and as illustrated, by providing an N:1 slotting ratio, wherein N>1, an assigned conventional or trunked traffic channel may allow a repeater such as repeater1 110 to receive or transmit voice and/or data for more than one call (up to N) on each frequency channel on which it is operating. In the example set forth in FIG. 1, repeater1 110 and repeater3 116 are each handling two calls on single respective frequencies in accordance with ETSI-DMR standard 2:1 slotting ratio.
In conventional repeater systems, separate frequencies are assigned for outbound (repeater→SU) and inbound (SU→repeater) transmissions. For example, to support full duplex calls for SU1 130, a fifth repeater (not shown) would need to be added to FIG. 1 that is time synchronized with repeater1 110 and that is assigned a fifth frequency that does not interfere with frequency1. Inbound traffic could then be sent to the fifth repeater by SU1 130 during TS1 on frequency1 and outbound traffic could then be sent to SU1 130 during TS2 on the fifth frequency. However, given the short guard intervals (˜2.5 ms) between time slots in accordance with the ETSI-DMR 6.25e standard, a typical SU cannot switch between frequency1 of repeater1 110 to transmit on TS1 and the fifth frequency of the fifth repeater to receive on TS2 within the time allotted under the standard. While the incorporation of a second synthesizer in the SU could alleviate some of the difficulty, the addition of a second independent synthesizer substantially increases the cost to manufacture a SU, the size and weight of the SU, and the power drain on the battery of the SU.
FIG. 2 illustrates an example 2:1 TDMA timing diagram 200 of a single inbound frequency air interface, such as that provided by repeater1 110, that operates in accordance with the ETSI-DMR 6.25e standard. Timeslot 1 202 includes 1.25 ms guard intervals 210, 212 and a 27.5 ms payload period 214 that includes a sync slot 216. Timeslot 2 204 similarly includes 1.25 ms guard intervals 220, 222 and a 27.5 ms payload period 224 that includes a sync slot 226. Timeslots 1 and 2 then repeat in an interleaved manner as illustrated in FIG. 2, including a second timeslot 1 206 for use by a same call 201 as used in timeslot 1 202, and another timeslot 2 208 for use by a same call 203 as used in timeslot 2 204, repeating in an interleaved manner until one or both calls end. Timeslots 1 202 and 2 204 together form a first frame 232, and timeslots 1 206 and 2 208 together form a second frame 234. Timeslot 1 202 could be, for example, equivalent to TS1 134 of FIG. 1 and may support a call 201 from SU1 130, and timeslot 2 204 could be, for example, equivalent to TS2 136 of FIG. 1 and may support a concurrent inbound call 203 from SU2 132.
What is needed is an improved method, system, and device for providing full duplex voice and data communications services in N:1 TDMA communications systems that does not require each SU to switch its synthesizer between a transmit frequency and a receive frequency (where the frequencies are different), and vice versa, within an amount of time between adjacent slots in the N:1 TDMA protocol.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.